Electron gun and support structure therefor



March 30, 1965 G. B. KUEHNE ETAL. 3,176,179

ELECTRON AND SUPPORT STRUCTURE THEREFOR Filed MaICh 26, 1962 INVENToRs GERHARD HAE B. KU MARTIN E, LEV/N ATTORNEY 3,17,l79 Patented Mar. IM), 196,5

United States Patent Office This invention relates to electron guns, and'particularly to an electron gun suitable for use in a klystron amplier in the 7.5 kilomegacycle frequency range capable of greater than 20 kilowatts C W. power output.

Because of the extremely small size of partsin a tube operating at this frequency, alignment between the radiofrequency structure and the electron gun structure is a serious problem. It is therefore one of the objects of this invention to provide means for aligning an electron gun with the associated radio-frequencyy structure in a manner to ensure substantially 100% transmission of the f electron beam from the gun through the radio-frequency structure. j

Another problem with electron guns is the tendency of electron gun electrodes to vibrate and thus cause `misalignment of the electron beam with the radio-frequency structure through which it is intended to pass. It is therefore one of the objects of this invention to provide an electron gun structure which is rigid and eliminates most vibration or microphonics from the structure.

It has been found that the electron gun structure, particularly the heater and cathode construction, are limiting factors in the life of an electron tube.A It is desirable in costly tubes such as the one for which the present gun is intended, that the electron gun be capable of being dismounted from the tube and thel internal parts thereof replaced, or a new gun attached to the tube. It is therefore another object of the invention to. provide a gun structure which is capable of being easily demounted from the remainder of the tube structure.

Since most high power tubes such as a klystron operating in X-band and having a 20 kilowatt CW. power output are operated at high voltages, it is desirable that the electron gun elements at elevated voltages be shielded in a manner to preclude accidental shorting of such'elements to ground, either Within or outside the vacuum. It is therefore another object of the present invention to support the electron gun structure in a manner completely shielding such structure from shorting to ground.

In a gun such as,V the one described for operation -in X-band, the cathode diameter is a scant one-half inch when a 50:1 convergence ratio is used, and all of the rej A i apparent from the following description and the drawings. It is to be understood, however, that the invention is not limited to the embodiments illustrated and described but may be embodied in Various forms within. the scope of the appended claims.

Broadly considered, the invention comprises a primary gun housing cylinder, preferably of metal, hermetically united at one end to the adjacent radio-frequency structure of the electron tube. The primary gun housing is preferably axially aligned with the accelerating anode and drift tube sections through which the beam will be projected. However, it is not critical that this element be exactly coaxially arranged with the axis of the anode and drift tubes for reasons which will appear. The end of the primary gun housing cylinder remote fromV the radio-frequency body structure is open and is adapted to receive therewithin the closed end of an auxiliary electron gun support shell fabricated from a dielectric such as alumina. The closed inner end of the dielectric support shell' is utilized as a base upon which to mount the focus electrode and cathode support shells in spaced relation to the grounded primary gun cylinder, and functions also as a part of the evacuated envelope. Axially spaced from the closed end of the dielectric support shell, the cylindrical skirt portion of the support shell is provided with a sealing and supporting structure interposed between the cylindrical skirt portion ofthe shell and the interior of the primary gun housing cylinder. This intervening sealing and support means is designed to pt*- mit accurate axial alignment of the cathode with the accelerating anode, and accurate transverse adjustment of the dielectric support shell with respect to the axis of the accelerating anode and drift tube sections so as to exactly align the electron gun with the structure through which the beam will be projected. The sealing and support structure is -preferably fabricated in a manner to provide for Heliarc welding of the dielectric support shell within the gun housing cylinder. a well known type of inert-gas, metal-arc welding technique using helium as the inert gas. To enclose and protect the outer end of the dielectric support shell against impact shocks, the outer end of the support shell is enclosed by an auxiliary end cap structure of metal which slips snugly around the outer end of the support shell and abuts against the sealing and support means, closing the end of the gun housing cylinder. Suitable detachable screw means interposed between the dielectricV support shell and the end cap structure securel the cap structure in position, the union between the auxiliary end cap structure and the support cup being such as to ensure Vthe absence of stress on the support cup. The end cap structure is also useful to provide for connection of input and output conductors which, inside the dielectric support shell or cup, are appropriately connected to the electron gun electrodes.

Referring to the drawing:

The single figure comprises a vertical half-sectional view of the electron gun structure, with a portion of the accelerating anode and radio-frequency structure to :which the gun attaches also illustrated. The View is shown approximately twice actual size.

In terms of greater detail, the electron gun of the invention comprises a primary gun housing cylinder 2, fabricated preferably from stainless steel, and having one end integrally brazed or united in a suitable manner to the magnetic pole piece member 3, which `also supports the accelerating anode or primarydrift tube section 4.. At its other end, the cylinder 2 is provided with a junction ring Vstructure 6, preferably annular in form and having a radially extending shoulder 7 against 'which the extreme end of thecylinder 2 may abut. The junction ring is hermetically lbrazed within the open end of the cylinder 2.

Within the cylinder 2, the junction ring is provided with a radially inwardly extending integral flange 8, having a flat radially extending annular surface 9 thereon. The junction ring is also provided with a cylindrical surface 11 substantially perpendicular to the surface 9. At its end remote from the cylinder 2, the junction ring is Heliarc welding `is .respect to each other. t

'prev'ded 'withVV a thin 'friet-anic fcyiindricauy extending cathode'. fromthe focus electrode. The opposite end of flange 12 having one end brazed hermetically to the junc- Y on the junction ring, theY surfaces are preferablyY machined after the junction ring andcylinderZ have been brazed to the pole piece member .3, vAtV this time the cylinder 2 with junction ring attached is chuckedin a lathe, and

theY surfaces 9V and 11 machined so,y that, respectviely,

the surface 9 is exactlyv perpendicularrtov the axis `of the surfaces 9 and v1 1 need not be exactly perpendicular withv Extending into the` 'primary ygun housing cylinder 2 through the central aperture in the annular junctional ring6 is "an auxiliary electron gun ksupport shell or cup 13, fabricated from ceramic or other suitable dielectric, having a cylindrical side Wall 14 and an end 'plateror wall 16.y 'The lend wall 16 is preferably brazed adjacent its outerperiphery to the inner end of the cylindrical side rwall 1,4 of Ythe support shell. ,For this purpose the end of the shell14 vand the peripheral surface of the end wall 16 are metalized. It will ofcourse be apparent to outfseams or joints.

in'confguration with the base end provided with a radially extendingange 19 suitably brazed to the peripheralredge `'of'fthe end Wall 16 of thesupport shell. Its apex end is Y providediwith Va cylindrical flange V241i,l to the outer periphery of which is spot-welded a junction ring21 having a cylindrical flange 22and a radially extending 'flange 23.

Ytion ring as shown. In forming the surfaces 9 and 11 'focus electrode.

the shell 38 is brazed about the youterfp'eriphe'ry of the This constructionV ensures that the expansion and contraction characteristics of different materials Will not cause buckling ofthe various members and thereby cause misalignment of these elements. Y

The heater, cathodeand focus electrodef'are suitably energized through leads 41 and 42'exte`nding'through an insulating member 43,*and having their outer ends connected by suitable strip connectors 44 and 46 to pin terminal members 47 and 48. The pin-terminal members f extend'throughY suitable apertures formed in end Wall 16 of the support shell, vandare brazed at their outer ends, on the opposite side of the end wall from the electron gun, into suitable terminal structures 49, as shown, which also g function to hermetically seal the aperture'in the end Wall those Yskilled inthe artthatthe cylinder 14 and end Wall v 16 may,'alternately,'be fabricated asa unitary dome With- 25V Forproper alignment of the electron gun components, Y

the height of the junction ringY 21 and flange 23 is`carefullyV gaugedwith respect to the surface 9 on. junction ring' 6. Additionally, the iiange 23 is oriented parallel to the surface 9 and therefore perpendicular'to the drift tubeaxis. The surface'94 on junction ring 6 thus serves Y as a reference plane. for all dimensions measured longipropriately supported on a cylindrical support shell 31 to reflect heat from the heater assembly 28 back` toward the cathode. At its end adjacentr the junction ring V21,

' the supportshell 31 is provided kWith a junction ring 32 having acylindrical ilange`33'and a radially extending anger34 which lies inabutting relation With'ange 23 on Vjunction ring 21,y In the fabricationof Vthe Vsub-V assembly'24, the distance between the -junction ring Yflange 34 and the cathode focus electrode assembly is carefully gauged sok that uponV being supported on the junction 'ring 21, these components will be properlyV spaced from reference surface 9; Once having -been manufactured as a subassembly meeting rigid specifica-L through Which lthe pin terminalA members extend. Within the shell 1S, Va suitable getter structureV 51 is connected to the shell at' one end and Yitsother endis connected to the terminal lead 47 in orderthat it may be appropriately energized to getter the inside of the electronV gun after it has been vacuumized. Because vaporized metal from the getter structure is' apt to provide a conducting layer on the surface 52 of vend plate ,16, and thereby short the leads 47 and 48, suitable shieldplates 53 are provided surrounding each of the pin terminal leads to prevent the migration of vaporized getter'material adjacent the leads at the point where they pass through the end plate 16.

i The shield plates are preferably provided with a radially extending ange portion 54 from vvhichisV struck a bead 56 adaptedV to abut against the surface 52 of ceramic wall 16 in a zone surroundingeach of the terminal leads.

The dielectric lsupport shell or cup 13 is supported Within the cylindrical metallic gun housingy 2 Vby a vacuum seal and support structure designated generally by the numeral 61; The seal and Asupport structure comprises a rst annular seal ring having-,an inner cylindrical flange 63 brazed about the outer peripheral surface ofthe cylinextending flange 64 integralV therevvith. The ange 64 is brazed-to one end of -a cylindrical dielectric spacer member 66 surrounding the cylindrical member 14, which r is brazed at itsother end to the radially extending iange vthe ends of the cylindrical member1'4. Brazed to the opposite side Yof the ange 67 from the spacer member 66 is a dielectric guide/and backing member 71, the surface `72 of which is accurately machined so as to lie atly against-the surface 9k formed on the junction ring 6.

In theV fabrication of the electron gun, this surface 72 tions,the subassembly 24`may be suitably jigged ,andY Y mounted on the junction ring 21 and junction ring flanges 23 and 24 united as by spot-welding. v It should be noted that the completedpsubassemblyzt is positioned on the junction ringl 21 by reference to surfaces 9l and 11 and not by reference .to the/junction ring 21. 'Y

As shown in the figure, thecathode and heater assembly are supported on axially'extending legs or struts 37 having one end spot-Welded to the end of the shell 31, and their other ends secured to the Vperipheral edge ofthe cathode. The focus electrode, on the other hand, is supportedonan auxiliary'shell 33 having `one end spot. Y

ofthe backing-member 71 vis Vmachined before the electron gun subassembly 24 hastbeen assembled on'the end wall 16.r Y Y Y Then, when the dielectric support shell with the gun structure supported thereon is inserted into the `gun cyl- Vexactly alignsitself withv the axis of the drift tube sections, the ldielectric supportcup 13 with the guide and positioning ring brazed thereonrfis suitably chucked in a latheand the outer `peripheral edgeVK 73 of the radially extending guide and positioning flange 67 is accurately machined circular and of the proper diameter so as to slidably-engage around'its entire periphery the cylindrical surface 11 formed on junctionv ringV 6. This operation is of course completed before the electron Vgun subassembly 24 is mounted on the support cup. y Then when the electron gun subassembly is jigged` and mounted on the support shell with reference to the accurately machined ange 67, and the entire assembly is then dropped into the junction ring assembly, the axis of the electron gun Vsubassembly will be accurately aligned with the drift tube axis. With the parts held in this position, the flange 12 on the junction ring 6 is appropriately Heliarcwelded to a cylindrical ange 74 having a radially extending plate portion 76 brazed to the flange 64. Backing member 77 of ceramic ensures integrity of this seal.

It will thus be seen that with the sealing and support structure 61 brazed and welded in position as described, 'the body of the support shell 13 is rigidly supported in spaced relation within the cylindrical housing member 2. To ensure that there Will be no transverse movement of the gun cup, with consequent misalignment of the electron beam, the outer end portion 78 of the support cup 13 is protected by a detachable metallic end cap structure 79 including a tubular portion 81 having one end in close sliding abutment against junction ring 6. Its other end is closed vby an end plate 82 having a shoulder 83 in its outer periphery forming a seat for the end of the tubular portion 81. The end cap structure is detachably secured to flange S4 cemented on the dielectric support shell 13, lthe ange being provided with suitable apertures threaded to receive screws 86 extending through end plate When the screws are tightened down, the end cap assembly is pulled into close association about the outer end of the support shell and junction ring 6 as shown. It should be noted that the flange 84 is only cemented to the support shell and that the screws 86 are of small size and of a soft material so as to ensure that the support shell will not be pulled out of alignment.

To energize the electron gun elements, a suitable pair of electrically conductive cables 87 are provided. The cables are preferably conventional cables having a copper braid 88 thereabout which in the present construction is doubled back and brazedto a supporting structure 89, which in turn is supported on the end plate 82 as shown. This serves to ground the braid of lthe cable to the electron gun body at a considerable distance from the connection of the inner conductor of the cable to the electron gun elements. In the figure, the section is taken through one of the cables, and the second cable is in the background and does not appear.

We claim:

1. An electron gun support assembly comprising a holloW rigid metallic housing portion, a hollow dielectric support shell closed at one end and having a Iside Wall extending into one end of said housing portion and hermetically united thereto to close said one end, an electron gun assembly including a cathode, heater and focus electrode mounted on the closed end of said dielectric support shell to project a beam of electrons along a longitudinal axis, and alignment means interposed between the housing portion and the hollow dielectric support shell to accurately set the longitudinal axis along which the beam is projected.

2. The combination according to claim l, in which the closed end of said hollow dielectric support shell lies within said housing portion.

3. An electron gun support assembly comprising a hollow rigid metallic housing portion, a hollow dielectric support shell closed at one end and having a side wall extending into one end of said housing portion and hermetically united thereto to close lsaid one end, an electron gun assembly including a cathode, heater and focus electrode mounted on the closed end of said dielectric support shell to project a beam of electrons along a longitudinal axis, alignment means interposed between the housing portion and the hollow dielectric support shell to accurately set the longitudinal axis along which the beam is projected, and a metallic end cap structure enclosing one end of said hollow dielectric support shell and detachably abutting said housing portion.

4. An electron gun support assembly comprising a hollow rigid metallic housing portion, a hollow dielectric support shell closed at one end and having a side wall extending into one end of said housing portion and hermetically united thereto to close said one end, said hollow dielectric support shell is open at one end and closed at its other end, the open end of said dielectric support shell lying outside said housing portion and the closed end lying intermediate the ends 'of said housing portion, an electron gun assembly including a cathode, heater and focus electrode mounted on the closed end of said dielectric support shell to project a beam of electrons along a longitudinal axis, said electron gun assembly being mounted on the side of said hollow dielectric support shell Wall opposite the open end thereof, and alignment means interposed between the housing portion and the hollow dielectric support shell to accurately set the longitudinal axis along which the beam is projected.

5. An electron gun support assembly comprising a hollow rigid metallic housing portion, a hollow dielectric support shell closed at one end and having a side wall extending into one end of said housing portion and hermetically united thereto to close said one end, an electron gun assembly including a cathode, heater and focus electrode mounted on the closed end of said dielectric support shell to project a beam of electrons along a longitudinal axis, and alignment means interposed between the housing portion and the hollow dielectric support shell to accurately set the longitudinal axis along which the beam is projected, said alignment means includes a junction ring xed adjacent said one end of said hollow metallic housing portion, said junction ring having a transverse annular guide surface thereon perpendicular to the longitudinal axis of said electron beam and a cylindrical guide surface thereon coaxial with the longitudinal axis of said electron beam, said electron gun assembly being mounted on said hollow dielectric support shell with reference to said guide surfaces and said longitudinal axis of said electron beam.

6. The combination according to claim 5, in which said alignment means includes a metallic guide ring brazed about the side wall of said hollow dielectric support shell intermediate its ends, and an annular ceramic backing member brazed to said metallic guide ring, the outer periphery of said metallic guide ring forming a snug slip t with said cylindrical guide surface on the junction ring and one surface of said ceramic backing member being adapted to lie atly against the transverse annular guide surface on the junction ring to axially align the longitudinal axis of the electron beam.

References Cited by the Examiner UNITED STATES PATENTS 2,583,121 1/52 Reynolds 313-237 X 2,967,260 l/ 61 Etel 3l3-82.l X 3,090,884 5/ 63 Morse 313-256 GEORGE N. WESTBY, Primary Examiner. 

1. AN ELECTRON GUN SUPPORT ASSEMBLY COMPRISING A HOLLOW RIGID METALLIC HOUSING PORTION, A HOLLOW DIELECTRIC SUPPORT SHELL CLOSED AT ONE END AND HAVING A SIDE WALL EXTENDING INTO ONE END OF SAID HOUSING PORTION AND HERMETICALLY UNITED THERETO TO CLOSE SAID ONE END, AN ELECTRON GUN ASSEMBLY INCLUDING A CATHODE, HEATER AND FOCUS ELECTRODE MOUNTED ON THE CLOSED END OF SAID DIELECTRIC SUPPORT SHELL TO PROJECT A BEAM OF ELECTRONS ALONG A LONGITUDINAL AXIS, AND ALIGNMENT MEANS INTERPOSED BETWEEN THE HOUSING PORTION AND THE HOLLOW DIELECTRIC SUPPORT SHELL TO ACCURATELY SET THE LONGITUDINAL AXIX ALONG WHICH THE BEAM IS PROJECTED, 